This invention relates to seismic surveying, and is more particularly but not exclusively concerned with methods and systems for providing a remote display representative of the coverage of a marine seismic survey while the survey is being carried out.
In order to perform a 3D marine seismic survey, a plurality of seismic streamers, each typically several thousand metres long and containing arrays of hydrophones and associated electronic equipment distributed along its length, are towed at about 5 knots behind a seismic survey vessel, which also tows one or more seismic sources, typically air guns. Acoustic signals produced by the seismic sources are directed down through the water into the earth beneath, where they are reflected from the various strata. The reflected signals are received by the hydrophones in the streamers, digitised and then transmitted to the seismic survey vessel, where they are recorded and at least partially processed with the ultimate aim of building up a representation of the earth strata in the area being surveyed.
One form of processing normally carried out on board the seismic survey vessel is processing to determine the coverage of the survey.
Thus the area of the survey is divided into cells, typically on a rectangular grid, each associated with a respective xe2x80x9cbinxe2x80x9d in which data relating to the cell is accumulated. As the survey processes, the seismic survey vessel tows the streamers to and fro along a number of spaced parallel lines that effectively form part of the rectangular grid, and that define continuous, or even slightly overlapping, parts of the area covered by the grid. At the same time, a dedicated processing system on board the vessel continuously calculates, from GPS-based positional information defining the respective positions of the source and hydrophone arrays at the time of each activation of the source, in which the respective reflection point (also known as the xe2x80x9ccommon mid-pointxe2x80x9d or CMP) giving rise to each trace produced by each hydrophone array lies, so that each trace can be assigned to the correct bin.
This on-board processing system builds up, substantially in real time, a data base containing the number of CMPs in each bin, along with their offset distribution (offsets being the respective distances between the source and the respective hydrophone arrays having CMPs in the bin). From this data base, several extremely informative displays are produced on the vessel, again substantially in real time, for example displays which show in contrasting colours those bins which contain less than a desired minimum number of CMPs and/or a high proportion of CMPs with large (or selected) offsets. Such displays are extremely useful for determining the coverage of the survey, and in particular, those parts of the area of the survey which may need to be xe2x80x9cfilled inxe2x80x9d, ie surveyed again.
Although this dedicated on-board processing system provides extremely useful information, in real time, to the survey crew on the vessel, it would be advantageous if the same information could be made available remotely, also substantially in real time, eg to the client who commissioned the survey.
It is an object of the present invention to provide such remote availability, and in a manner which is capable of being made highly secure.
According to a first aspect of the present invention, there is provided a method of providing a remote display representative of the quality of the coverage of a seismic survey, the method comprising the steps of:
(a) progressively building up at the site of the survey a first data base of data required for said display and relating to the area being covered by the survey;
(b) concurrently transmitting the data being used to build up the first data base via satellite link to a first remote location, to build up a duplicate of the first data base at said first remote location;
(c) providing access to said first remote location for the receipt of display requests from further remote locations; and
(d) in response to such a request, processing the data of said duplicate data base to provide processed data for producing said display, and compressing said processed data and transmitting it to such a further remote location for reconstitution and display thereat.
According to another aspect of the invention, there is provided a system for providing a remote display representative of the quality of the coverage of a seismic survey, the system comprising:
(a) means for progressively building up at the site of the survey a first data base of data required for said display and relating to the area being covered by the survey;
(b) means for concurrently transmitting the data being used to build up the first data base via satellite link to a first remote location;
(c) means for receiving the transmitted data and building up a duplicate of the first data base at the first remote location; and
(d) processing means at the first remote location for processing the data of said duplicate data base to provide processed data for producing said display, said processing means including means responsive to requests from further remote locations to provide and compress such processed data and transmit it to such further remote locations for reconstitution and display thereat.
In preferred implementations of either aspect of the invention, the data required for said display includes data related to the number of CMPs, and/or data related to offset distribution, per unit area of the area being surveyed.
FIG. 2 shows a flowchart 200 illustrating a method of one embodiment of the present invention. The method involves progressively building up at the site of the survey a first data base of data required for the display and relating to the area being covered by the survey (at 210). The data being used to build up the first data base is concurrently transferred via satellite link to a first remote location, to build up a duplicate of the first data base at the first remote location (at 220). The method also provides access to the first remote location for the receipt of display requests from further remote locations (at 230), and in response to such requests, processes the data of the duplicate data base to provide processed data for producing the display and compresses the processed data for transmission to such a further remote location for reconstitution and display thereat (at 240).
Advantageously, at least part of a program used for said processing is transmitted to said further remote location along with said compressed data, to permit further processing at said remote location.
Conveniently, said processing is performed using a Java application program.
Preferably, access to said first remote location is protected, eg by requiring the use of a user-name and password, or a digital client certificate, or a smart card or other physical security device (or xe2x80x9cdonglexe2x80x9d), while communication between said first remote location and said further remote location is preferably encrypted.